Re: Interrupt handlers and mutex

[Matt Thomas <matt%3am-software.com@localhost>]

On Dec 31, 2009, at 2:33 PM, Frank Zerangue wrote:

> Matt,
> 
> Item (2) below when you say "That can't happen" , is that because the LWP 
> that holds the mutex has also changed the IPL? If so, why the need for the 
> interrupt handler to acquire the mutex? Otherwise, could you expound on item 
> (2) because I am missing something?

Yes.  Because that LWP might be on another CPU.

If the LWP is running on the same CPU as the interrupt, IPL exclusion also 
applies because the LWP is running at the IPL of the mutex before trying to 
acquire the mutex.  If LWP is on a different CPU, the mutex itself prevents 
concurrent access.